Pb-Bi-Sr-Ca-Cu-oxide powder mix with enhanced reactivity and process for its manufacture

ABSTRACT

An Oxide Precursor Powder from the Pb—Bi—Sr—Ca—Cu—O 2223 System can be produced by heat treating powder, produced using the Spray Pyrolysis Process as described in: GB2210605 or EP0681989 between 700° C. and 850° C. in an atmosphere containing between 0.1% and 21% O 2 . Heat Treatment of the pyrolysis powder under controlled conditions produces a powder with a particular phase composition, that is highly homogeneous and has a small particle size distribution, that is inherently more reactive than powders heat treated in the same way but produced using other processes.

This invention relates to mixed oxide powder mixtures with enhancedreactivity as presursor materials for superconductors and to a processfor its manufacture.

In special the present invention relates to precursor powders producedby spray pyrolysis that are then further heat treated such that theyshow considerable advantage in forming the Pb—Bi—Sr—Ca—Cu—O 2-2-2-3superconducting phase over powders produced using other routes.

Superconductors are materials that loose all resistance to the flow ofelectricity below a critical transition temperature. Todaysuperconducting metals and alloys are being used in a variety ofcommercial applications in Electronics and Medicine, for example the useof Low Temperature Superconducting Magnets in MRI (Magnetic ResonanceImaging) systems and as Electromagnets in High Energy Physics. Thediscovery of Superconductivity in the Ceramic Oxide System La—Sr—Cu—Osystem in 1986 (ref Berdnoz und Müller: Z. Physik B 64, 189, 1986)sparked renewed activity in the search for Super-conductivity attemperatures above those only then accessible with liquid helium. Withinone year the ‘High Temperature’ Y—Ba—Cu—Oxide system (HTS) had beendiscovered in which the critical transition temperature had been raisedabove 77K (ref Chu: EP341266, 12.01.87), allowing liquid nitrogen to beused as a coolant. Many new High Temperature Superconductors have beendiscovered and evaluated for potential commercial application over thelast ten years, but still the two systems regarded as having thegreatest chance of commercial success in the near future are thosesystems discovered the first, the ‘Re’(Rare Earth) —Ba—Cu Oxides andthose based on the Bi—Sr—Ca—Cu Oxide Sytem.

The current market share for the High Temperature Superconductors withinthe Superconductor Industry is small at ca 3% (15M) of the total (refBCC Market Research Study: GB-106R, The Superconductor Industry). Thisis because these Materials and Systems are still in the development andprototype stage, real market growth expected only after the systems haveproved themselves to have advantage both in cost and quality(performance and environmental impact). The largest market segment forHTS is currently in elec- tronics and communications where they are usedas microwave filters and resonators. Other segments where both theRe—Ba—Cu—O and Bi—Sr—Ca—Cu—O systems are under development includeCurrent Leads to provide low loss energy supply to LTS systems, MagneticEnergy Storage devices able to supply energy when routine supply hasbeen interrupted, Fault Current Limiters to reduce energy supply to aload during a fault, Magnet Systems, Power Cables,Motors and Generators.Wires and Tapes, for use in a number of the afore-mentionedapplications, continue to be developed based on the Pb—Bi—Sr—Ca—Cu—O2-2-2-3 system. In competition, the IBAD and RaBITs Process using theRe—Ba—Cu Oxides are also now attracting more attention (X. D. Wu et al,Applied Physics Letters 65, 1961, 1994).

The current prefered method to manufacture Pb—Bi—Sr—Ca—Cu—O 2-2-2-3tapes for energy applications is to use the oxide Powder in Tube method(PIT Method). This process involves the packing of a precursor form intoa silver alloy tube that is then subject to repeated mechanicaldeformation and high temperature thermal treatments. The final productconsists of thin filaments of sintered ceramic within the silver-alloyhost. During the heat treatment process the precursor form within thesilver matrix undergoes conversion to the desired superconducting phase,the Pb—B—Sr—Ca—Cu—O 2-2-2-3 phase (ref EP0330305, Jan. 19, 1989; U.S.Pat. No. 4,880,771, Feb. 26, 1988). The quality of the final tapes isdependent upon many process parameters, including the intrinsic natureof the precursor powder, the density of the powder preform, the natureof the silver alloy sheath, the reduction on passing through the drawingdie, pressing versus rolling, number of filaments, the calcinationatmosphere, the calcination temperature, the calcination time and theheating and cooling cycles. As the processes within the tape during theheat treatments involve chemical conversion to the prefered 2-2-2-3phase, the intrinsic properties of the precursor powder determine, to adegree, the choice of processing parameters. The conversion of thepowder to the 2-2-2-3 phase is thought to proceed via one of two routes,either by growth of the 2-2-2-3 phase from a liquid phase (Flukiger etal, SST, 10, A68, 1997) or by intercalation of calcium and copper oxidelayers into the 2-2-1-2 crystal grains already present in the precursorpowder (J Jiang, S Abel, SST 10,1997, 678 and references therein).Therole of the deformation step in the processing of these tapes is to bothtexture the grains and to increase the density within the ceramic core.However this step can also introduce cracks and defects in the ceramicwhich have to be healed during the thermal processing. The liquid phase,produced by melting of particular phases, for example induced throughreaction with calcium plumbate, is thought to accelerate phaseconversion as well as to both heal these microcracks and remove unwantedgrain bounday phases. Therefore the relative amounts of these phasesneed to be controlled, both in the original precursor itself and throughthe processing stages to supply enough liquid phase to the system andthereby produce clean grained, well aligned 2-2-2-3 grains at the end ofthe process. One of the first stages during this conversion is theincorporation of lead from the plumbate phases into the Bi-2-2-1-2grains. This can be followed by monitoring the change in the phasecomposition of the material, by for example X-Ray Diffraction. As thereaction proceeds, the calcium plumbate levels decrease as lead entersinto the Bi-2-2-1-2 grains. This also results in a change of the latticetype that can be followed with X-Ray Diffraction, changing from atetragonal unit cell to an orthorhombic one. Too much calcium plumbateis thought to be detrimental to the formation of well textured 2-2-2-3grains. Excess calcium plumbate can give rise to the growth ofundesirable alkaline earth phases during the processing which cannot beremoved at a later stage, can disrupt the layering of the 2-2-2-3 grainsduring mechanical deformation and can decompose, releasing gas, that istrapped momentarily within the silver alloy sheath and results inirrecoverable deformation of the tape. It is also thought that toolittle calcium plumbate is detrimental in PIT processing because notenough liquid phase can then be supplied during the heat processingstages to heal all the microcracks, clean all the grain boundaries andfacilitate the final conversion of residual phases to 2-2-2-3. The finalreaction step involves conversion of the lead containing 2-2-1-2 intothe 2-2-2-3 phase (R. Flukiger et al, Superconducting Science andTechnology 10(1997) A68-A92.

Those powders commonly considered for use as precursors can bemanufactured by a number of routes. These include routes starting fromsolid components, eg the ‘mix and grind’ process and those routesstarting from solutions, eg: citrate gel (U.S. Pat. No. 5,066,636),co-precipitation (U.S. Pat. No. 5,147,848) and spray pyrolysis (GB8723345).

Although these processes have been applied to the synthesis ofsuperconducting powders there is no systematic procedure for acontrolled conversion into the 2-2-2-3 phase of powders produced by anyof these routes.

Therfore, there was a need for a method for the synthesis ofsuperconducting powders comprising a controlled conversion into the2-2-2-3 phase of powders produced.

A solution has been found by a process to manufacture a mixedPb_(u)Bi_(v)Sr_(w)Ca_(x)Cu_(y) oxide powder in which a mixed-metalsolution is sprayed as a fine mist into a heated reactor between 600° C.and 1200° C. and the collected powder subsequently calcined between 700° C. and 850° C. under an atmosphere of between 0.1% oxygen and 21%oxygen for a total heating time at maximum temperature between 4 and 180hours.

A part of the present invention is a powder prepared according to thisprocess, in which the compositions for this precursor powder is Pb(0.2-0.4) Bi (1.6-2.0) Sr (1.7-2.0) Ca (1.7-2.3) Cu (1.8-3.3) Ox.

The superconducting phase prepared according to the claimed process inwhich the mixture, as identified by X-ray diffraction techniques,contains one or more than one of the oxides or mixtures of the group(Bi_(1−s)Pb_(s)) 1.7-2.4 (Sr_(1−t)Ca_(t)) 2.6-3.3 Cu 1.8-2.2 O_(x) phase(abbreviated to 2-2-1-2 phase with s=0-0.4, t=0.2-2.0),(Ca_(1−m)Sr_(m))₂PbO₄ (where m=0-1), (Sr_(14−w)Ca_(w))Cu₂₄O₄₁(abbreviated to 14-24 phase with w=0-9), (Ca_(1−u)Sr_(u))_(1−n)CuO_(x)(1-1 phase with n=0-0.3, u=0-0.3), (Pb_(1−x)Bi_(x)) 2.9-3.4(Sr_(1−y)Ca_(y)) 4.7-5.0 Cu 0.7-1.2 O_(z) (abbreviated to 3-3-2-1 phasewith x=0-0.4, v=0-0.5), CuO, (Sr,Ca)O, (Bi_(1−z)Pb_(z)) 2.0-2.6 (Sr,Ca)1.4-1.9 Cu 1.8-2.2 O_(x) (abbreviated to 2-2-0-1 phase with z=0-0.3),(Ca_(1−p)Sr_(p))2CuO_(x) (abbreviated to 2-1 phase with p=0-0.3), Bi6Sr8.5−rCa 2.5+rO_(x) (abbreviated to 9-11-5 with r=0.0-2.2) and(Bi_(1−y)Pb_(y)) 1.8-2.3 Sr 1.6-1.9 Ca 1.6-2.0 Cu 2.6-3.1 O_(x)(abbreviated to 2-2-2-3 phase with y=0-0.4).

A precursor powder prepared according to this process may contain saidphases in which the weight % of these phases, as determined using theRietveld Method described later, are 2-2-1-2 phase: 60-95%, and/or 2-1phase: 0-24%, and/or 14-24 phase: 0-20%, and/or 9-11-5 phase. 0-18%,and/or (Ca_(1−m)Sr_(m))₂PbO₄: 0-15%, and/or 3-3-2-1 phase: 0-14%, and/orCuO: 0-11%, and/or 1-1 phase: 0-10% and/or CaO: 0-7%

A precursor powder prepared according to the Process of the presentinvention in which the lead, has entered into the 2212 grains is also amatter of this application as well as a precursor powder in which thecarbon content of said powder is under 500 ppm and the use of thepowders prepared for the manufacture of superconducting artefacts.

In summary an Oxide Precursor Powder from the Pb—Bi—Sr—Ca—Cu—O 2-2-2-3system can be produced by heat treating powder, produced using the SprayPyrolysis Process as described in: GB2210605 or EP0681989 between 700°C. and 850° C. in an atmosphere containing between 0.1% and 21% O₂. Heattreatment of the pyrolysis powder under controlled conditions produces apowder with a particular phase composition, that is highly homogeneousand has a small particle size distribution, that is inherently morereactive than powders heat treated in the same way but produced usingother processes. This is to be demonstrated in the detailed descriptionbelow.

It has been found by experiments that the powder produced by the spraypyrolysis process and which was further heat treated to produce aprecursor offers significant advantages over those produced by the otherroutes. In particular the precursor produced from spray pyrolysis powderaccording to the invention is more reactive, conversion to the 2-2-2-3phase is faster and thereby saves time and cost, over those produced bythe other routes. The precursor produced has a more homogeneous phasedistribution and smaller primary particle size than those produced bythe other methods.

Under controlled conditions the carbon levels in the powder could alsobe maintained at a low level, under 500 ppm.

The grain growth on calcining the fine grained pyrolysis powder canoften result in powders with primary particles not larger than the rawmaterial components used in the solid state manufacturing process.

An important advantage of the present invention is, that a highlyhomogeneous powder containing a mix of at least five crystalline phases,each with a small primary particle size is received that reacts byforming the 2-2-2-3 superconducting phase faster than those equivalentpowders produced using the citrate gel, co-precipitation and solid statetechniques (ref Patents: Liu: U.S. Pat. Nos. 5,066,636, 5,147,848). Themain advantage is that the user of such powders requires less time toform the required 2-2-2-3 superconducting phase, saving time and cost inmanufacturing their artefacts. This is of particular relevance to the‘powder in tube’tape manufactures producing 2-2-2-3 tapes (Sandhage etal, Journal of Materials, Vol 43, No 3, 1991).

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preferred specific embodiments and examples are,therefore, to be construed as merely illustrative, and not limitative ofthe disclosure in any way whatsoever.

The entire disclosures of all applications, patents, and publicationscited above and below are hereby incorporated by reference.

The preparation according to the present invention is as follows:

SAMPLE PREPARATIONS

(1) Spray Pyrolysis Powder was produced from a mixed nitrate solution oflead, bismuth, strontium, calcium and copper with the nominal ratio: Pb0.4: Bi 1.7: Sr 1.8: Ca 2.2: Cu 3.2. The nominal concentrationcorresponded to 100 g mixed-metal oxide per 1000 ml water. For each 100g of (Bi_(1.7)PbO_(0.4))Sr_(1.8)Ca_(2.2)Cu_(3.2)O_(x) the followingamounts of nitrates were combined: 78.552 g of Bi(NO₃)₃.5H₂O, 12.62 g ofPb(NO₃)₂, 36.286 g of Sr(NO₃)₂,49.49 g of Ca(NO₃)₂.4H₂O, 73.646 g ofCu(NO₃)₂.3H₂O.

By using the same method, with the appropriate mixture of raw nitrates,a powder of the nominal composition: Pb 0.33 Bi 1.80 Sr 1.87 Ca 2.00 Cu3.00 Ox was also produced.

The solution was sprayed into a stainless steel reactor of 80 mmdiameter and 1 m long, using a two fluid sprayhead with air feed of0.34-0.52 bar. The solution was delivered to the sprayhead using a pumpand the reactor temperature was between 800° C. and 1000° C. The averagedroplet size, d₅₀, was <2 microns. The resulting powder was collected bypassing the exhaust gas stream through a Pall. stainless steel filterwith a mesh size of approximately 5 microns. Approximately 400 g ofpowder was collected over a 24 hour period.

(2) Co-Precipitation Powder was prepared from a nitrate solutioncorresponding to the same nominal composition as (1).

For each 5 g of (Bi_(1.7)Pb_(0.4))Sr_(1.8)Ca_(2.2)Cu_(3.2)O_(x) thefollowing amounts of nitrates were combined: 3.9276 g of Bi(NO₃)₃.5H₂O,0.6310 g of Pb(NO₃)₂, 1.8143 g of Sr(NO₃)₂, 2.4745 g of Ca(NO₃)₂.4H₂O,3.6823 g of Cu(NO₃)₂.3H₂O and 40 ml of nitric acid (HNO₃, 1.66M). Themetal nitrates were dissolved into nitric acid. 7.3106 g of oxalic acid(H₂C₂O₄) was dissolved in 75 ml of ionized water. 11.7426 g oftriethylamine (C₆H₁₅N) was then added to the solution. The pH value ofthe triethylamine/oxalic acid solution was 4.3˜4.2.

The metal nitrate solution was titrated into triethylamineloxalic acidsolution, until all of the metals precipitated out. The final pH valueof precipitates was about one.

The sample was then filtered and dried at 80 degrees centigrade andfinally heat treated at 200 degrees centigrade for 24 hours.

(3) Citrate Gel Powder was prepared whereby 1 g equivalent of citricacid was added to a nitrate solution, with the same concentration as (1)

For each 5 g of (Bi_(1.7)Pb_(0.4))Sr_(1.8)Ca_(2.2)Cu_(3.2)O_(x) thefollowing amounts of nitrates were combined: 3.9276 g of Bi(NO₃)₃.5H₂O,0.6310 g of Pb(NO₃)₂, 1.8143 g of Sr(NO₃)₂, 2.4745 g of Ca(NO₃)₂.4H₂O,3.6823 g of Cu(NO₃)₂.3H₂O and of 10 ml nitric acid (HNO₃, 70%)

Metal nitrates were dissolved in nitric acid, ionized water was thenadded till the total volume of the solution reached 50 ml. 6.7726 g ofCitrate acid (C₆H₈O_(x).H₂O) was added into the metal nitrate solution.Finally we slowly added ethylenediamine (C₂H₈N₂, 99%) to the solutionuntil its pH value reach 6. The solution was then heated at 100° C.until a gel forms. and subsequently heat treated at 200 degreescentigrade for 24 hours.

(4) Powders prepared using the conventional solid state route whereproduced by intimately mixing appropriate amounts of Bismuth Oxide, LeadOxide, Copper Oxide, Strontium Carbonate and Calcium Carbonate. For each5 g of (Bi_(1.7)Pb_(0.4))Sr_(1.8)Ca_(2.2)Cu_(3.2)O_(x) 1.9803 g Bi₂O₃,0.4464 g PbO, 1.3287 g SrCO₃, 1.1010 g CaCO₃ and 1.2728 g CuO wheremixed.

All the above powders are then heat treated together using the followingprocess:

Heat treatment at 730° C. for 24 hours followed by two 24 hour heattreatments at 800° C. and finally four heat treatments at 842° C. In allcases the heating rate of the furnace was 1° C. per minute and thecooling rate was the natural cooling rate of the furnace.

The X-Ray diffraction traces of the precursor powders of nominalcomposition: (Bi_(1.7)Pb_(0.4))Sr_(1.8)Ca_(2.2)Cu_(3.2)O_(x) producedare shown in FIGS. 1a and 1 b. In the case of the precursor powderproduced by Spray Pyrolysis the phases present are the 2-2-1-2 phase,Ca₂PbO₄, the 14-24 Phase, the 1-1 phase, CuO and the 3-3-2-1 Phase.

The powders produced by the other methods contain other phases includingCopper free phases and significantly more CuO.

The relative amounts of particular secondary phases can be comparedusing the X-Ray diffraction data and this is shown in FIG. 2. Theprecursor produced by Spray Pyrolysis contain very small amounts ofCopper Oxide and contains the smallest amount of Calcium Plumbate phase.

The compositions of the powders are shown in Table 1, showing that thepowder prepared by co-precipitation is very deficient in strontium andcalcium and has excess copper and lead. This was to be expected whereprecipitation of each component is dependent upon pH.

TABLE 1 Composition of the precursor powders ICP (Molar Ratio) MaterialBi Pb Sr Ca Cu Expected Composition 1.70 0.40 1.80 2.20 3.20 Spray 1.690.38 1.78 2.18 3.30 Co-precipitation 1.79 0.42 1.65 1.88 3.57 Citrategel 1.66 0.39 1.79 2.16 3.30 Solid-state 1.68 0.39 1.79 2.20 3.23

To measure the reactivity of the powder, the development of the final2-2-2-3 phase was monitored using X-Ray Diffraction. These results canbe seen in FIG. 3a and 3 b. By comparing the intensities of linesrelating to the phases 2-2-2-3 and 2-2-1-2 it is possible to determinethe extend of conversion to 2-2-2-3, as shown in FIG. 4. The precursorproduced from the Spray Pyrolysis powder converts to the 2-2-2-3 phasemuch faster than those produces using the other routes.

The reactivity of the powder produced by this method is determined by anumber of parameters including the particle size of the startingprecursor. In FIG. 5 it is clearly shown that the particle size of thepowder produced by the spray pyrolysis powder is finer than thoseproduced using the other methods. Further it has been shown, that thelarge particles as visible in the micrographs for powders manufacturedby the other routes, can be secondary phases, for example calciumplumbate and copper oxide that may take longer to react than if formedas a finer phase.

Another important factor relating to the reactivity is the phasecomposition of the precursor powder. Precursor Powders produced by theSpray Pyrolysis process vary from the others in having very little or nocopper oxide phase, less calcium plumbate phase and significant amountsof (Sr_(14−v)Ca_(v))Cu₂₄O₄₁ phase. The reduced amount of calciumplumbate phase indicates that substantial amounts of plumbate havealready been consumed resulting with lead entering into theBi—Sr—Ca—Cu—O 2-2-1-2 phase. The particular phase mixture formed in thisprocess, with smaller amounts of calcium plumbate, leadcontaining-2-2-1-2 and calcium cuprates is ideally suited, as has beendemonstrated, to forming the 2-2-2-3 phase much faster than the otherphase mixtures.

The phase weight percentages were determined by the Rietveld methodaccording to Hill and Howard (1987) using X-ray diffraction.Commensurate approximations to all crystal structures where used and thestructure parameters were fixed to the literature value (Miehe et al,Phsica C 171, 339,1990 for the 2-2-2-3 phase, Petricek et al, Phys. Rev.B 42, 387,1990 for the 2-2-1-2 phase, von Schering et al, Angew. Chem.100, 4, 1988 for the 2-2-0-1 phase, Teichert and Müller-Buschbaum,Z.anorg. alIg. Chem. 607 128, 1992 for the (Sr/Ca)2PbO4 phase, Kim etal, J. Sol. State Chem. 85, 44, 1994 for the 3-3-2-1 phase, Babu andGreaves, Mat. Res. Bull. 26, 499, 1991 for the 1-1 phase, Siegrist etal, Mat. Res. Bull 23, 1429, 1988 for the 14-24 phase, Heinau et al, Z.Krist 209, 418, 1994 for the 2-1 phase, Asbrink and Lorrby Acta, Cryst B26, 8, 1970 for CuOI, Primak et al, J. Am. Chem. Soc. 70, 2043, 1948 for(Sr,Ca)O and a revised version of Luhrs et al, Chem. Matters. 10, 7,1875, 1998 for the 9-11-5 phase) Refined parameters were the latticeconstants, Pseudo-Voight peak profile parameters including [uvw]description of peak width, 2-2-1-2 grain alignment using the March Modeland an overall temperature factor. Microabsorption effects wereneglected.

The advantageous results received according to the present invention areshown in FIGS. 1a-5.

FIG. 1a: X-Ray diffraction traces of the precursor powders

FIG. 1b: XRD trace showing the positions of the, various phases presentin the powder diagram: vertical lines=2-2-1-2 phase (Pdf Card 40-0378;line 1=Calcium Plumbate (CA₂PbO₄); line 2: 3-3-2-1 phase; line 3:Ca₇Sr₇Cu₂₄O₄₁, line 4: Ca_(0.83)CuO₂

FIG. 2: The relative intensities of the calcium plumbate and copperoxide peaks as seen in the X-Ray diffractogram

FIG. 3a: XRD diagram of the Phase Development after 24 hours at 842° C.

FIG. 3b: XRD diagram of the Phase Development after 72 hours at 842° C.

FIG. 4: The phase formation of Bi-2-2-2-3 with sintering hours. A₂₋₂₋₂₋₃and A₂₋₂₋₁₋₂ denote the areas of the diffraction peaks of Bi-2-2-2-3(0010) and Bi-2-2-1-2 (008) phases, respectively. The nominalcomposition of Merck A is(Bi_(1.7)Pb_(0.4))Sr_(1.8)Ca_(2.2)Cu_(3.2)O_(x) and Merck B is(Bi_(1.8)Pb_(0.33))Sr_(1.87)Ca₂Cu₃O_(x).

FIG. 5a: Scanning Electron Micrographs of Powder prepared using spraypyrolysis

FIG. 5b: Scanning Electron Micrographs of Powder prepared usingcoprecipitation

FIG. 5c: Scanning Electron Micrographs of Powder prepared using citrategel

FIG. 5d: Scanning Electron Micrographs of Powder prepared using solidstate.

What is claimed is:
 1. An oxide precursor powder of the formula havingPb_((0.2-0.4))Bi_((1.6-2.0))Sr_((1.7-2.0))Ca_((1.7-2.3))Cu_((1.8-3.3))O_(x),having phase comprising one or more than one of oxides or mixtures ofthe group(Bi_(1−s)Pb_(s))_(1.7-2.4)(Sr_(1−t)Ca_(t))_(2.6-3.3)Cu_(1.8-2.2)O_(x)phase, abbreviated to 2-2-1-2 phase with s=0-0.4, t=0.4-2.0,(Ca_(1−m)Sr_(m))₂PbO₄ (where m=0-1), (Sr_(14−w)Ca_(w))Cu₂₄O₄₁,abbreviated to 14-24 phase with w=0-9, (Ca_(1−u)Sr_(u))_(1−n)CuO_(x),1-1 phase with n=0-0.3, u=0-0.3,(Pb_(1−x)Bi_(x))_(2.9-3.4)(Sr_(1−y)Ca_(y))_(4.7-5.0)Cu_(0.7-1.2)O_(z),abbreviated to 3-3-2-1 phase with x=0-0.4, y=0-0.5, CuO, (Sr,Ca)O,(Bi_(1−z)Pb_(z))_(2.0-2.6)(Sr,Ca)_(1.4-1.9)Cu_(1.8-2.2)O_(x),abbreviated to 2-2-0-1 phase with z=0-0.3, (Ca_(1−p)Sr_(p))₂O_(x),abbreviated to 2-1 phase with p=0-0.3, Bi₆Sr_(8.5−r)Ca_(2.5+r)O_(x),abbreviated to 9-11-5 with r=0.0-2.2, and(Bi_(1−y)Pb_(y))_(1.8-2.3)Sr_(1.6-1.9)Ca_(1.6-2.0)Cu_(2.6-3.1)O_(x),abbreviated to 2-2-2-3 phase with y=0-0.4, prepared in a process inwhich a mixed-metal solution is sprayed as a fine mist into a heatedreactor between 600° C. and 1200° C. and the collected powdersubsequently calcined between 700° C. and 850° C. under an atmosphere ofbetween 0.1% oxygen and 21% oxygen for a total heating time at maximumtemperature between 4 and 180 hours to yield the oxide precursor powder.2. An oxide precursor powder according to claim 1, in which the weightpercents of phases are 2-2-1-2 phase: 60-95%, and 2-1 phase: 0-24%, and14-24 phase 0-20%, and 9-11-5 phase: 0-18%, and (Ca_(1−m)Sr_(m))₂PbO₄:0-15%, and 3-3-2-1 phase: 0-14%, and CuO: 0-11%, and 1-1 phase: 0-10 %and CaO: 0-7%.
 3. An oxide precursor powder prepared according to claim1 not containing phases free of copper oxide or copper.
 4. An oxideprecursor powder according to claim 1 which the lead has entered into2-2-1-2 gains.
 5. An oxide precursor powder according to claim 1 inwhich the carbon content of said powder is under 500 ppm.
 6. An oxideprecursor powder according to claim 1 comprising the 2-2-2-3 phase. 7.An oxide precursor powder according to claim 1 in which the averageprimary particle size is between 1-4 microns.
 8. A process formanufacturing a super-conducting artefact comprising mechanicallydeforming and thermally treating an oxide precursor powder according toclaim 1.